In order to meet fuel efficiency standards and/or customer fuel economy expectations, efforts have been made to reduce the weight of vehicles (e.g., light-weighting). One approach to light-weighting has included substituting lighter materials for traditional materials, for example, using aluminum instead of steel for some components. Additionally, stronger grades of steel reduce vehicle mass by enabling more efficient designs requiring less steel. These substitutions and strategies may also be mixed, leading to situations where dissimilar materials need to be joined. However, difficulties in joining the dissimilar materials may limit the utilization of lighter weight materials. For example, there may be difficulties in the welding and joining processes when components formed of aluminum and high strength steel need to be joined.
One current solution for mechanical joining of dissimilar materials is the use of self-piercing rivets (SPRs). In general, the SPR process includes clamping two or more sheets between a die and a blankholder and driving a semi-tubular rivet into the materials between a punch and die in a press tool. The SPR pierces the top sheet and flares into the lower sheet to mechanically interlock the sheets. Riveting aluminum alloys with advanced high-strength steel (AHSS) or ultra high-strength steel (DHSS), such as boron steel, can be challenging due to high strength/low ductility of the AHSS or boron steel after hot stamping.